Filter element for filtering fluids

ABSTRACT

The invention relates to a filter element for filtering fluids, comprising at least one filter unit ( 12, 14,16 ) that is disposed concentrically around the axis of said element, said unit being supported on at least one supporting element ( 24, 26, 30 ) in the direction of flow of the fluid. According to the invention, at least part of the supporting elements ( 24, 26 ) is provided at least on the side facing the filter unit ( 12, 14, 16 ) with channels ( 28 ) for guiding the fluid. Longitudinal ribs ( 50 ), which delimit said channels ( 28 ), extend along the supporting element ( 24, 26 ) in the form of spiral tracks. The two free ends of each channel ( 28 ) emerge at opposite ends of the corresponding supporting element ( 24, 26 ). The channels ( 28 ) extend continuously along the supporting element, are devoid of multiple deviations in the fluid flow and only partially surround the corresponding supporting element ( 24, 28 ), thus forming a torsional, guide for the fluid flow.

The invention relates to a filter element for filtering fluids with atleast one filter unit which is arranged concentrically around itslongitudinal axis, and which is supported in the direction of therespective throughflow of the fluid stream on at least one supportelement, at least some of the support elements being provided at leaston their side facing the filter unit with channels for guiding thefluid, the channels extending with their longitudinal ribs which borderthem in spiral tracks along the support element, and the respectivechannel with its two free ends emerging on the opposing ends of therespective support element.

DE-A-198 37 257 discloses as a filter element a filter module which issimplified with respect to its structure and also enables production ofa stage filter. Each layer of the filter medium as the filter unitconsists of a bed of deep-bed filter material, these beds alternatingwith spacers, consisting of individual draining beds, which are stackedtogether with the filter beds without gaps horizontally on top of oneanother transversely to the longitudinal axis of the filter module. Thedraining beds are sealed on alternate sides to the filtrate/unfilteredmaterial chamber, with the known approach any arrangement of filter bedsbeing attainable.

By using beds both for the spacers and also for the filter layers, theknown approach makes it possible to stack all beds horizontally withoutthe need for separate support elements for example in the form ofsupport tubes here, as is generally the case for conventional filterelements. Moreover it is possible to stack any filter beds withdifferent filter fineness in any sequence.

But it has been shown in practice that the known filter element can failespecially at high pressures of the fluid which is to be filtered, forexample because the deep-bed filter material beds cannot be adequatelysupported on the spacers in the form of draining beds. The latter canlead to failure of the entire filter element.

EP-B-0 817 668 discloses a filter device which preferably is designed asa bypass flow filter assembly and is used specifically for filtration ofhydraulic oil supplies with a motor-driven pump and a permanentlymounted filter housing which may be closed with a cover. The filterhousing has an interchangeable filter element through which flow cantake place from the inside to the outside and which has two cylindricalfilter units which are arranged concentrically to its longitudinal axis,which filter units have a radial distance between themselves, and whichare held on the end side at least by different cover parts. Theunfiltered material which is introduced between the radial spacing ofthe two filter units is routed in both directions through therespectively assigned filter unit and is filtered in such a manner.Accordingly the filter units, with the formation of the generic priorart, are enclosed to the inside and to the outside by a support elementin the form of a support tube which is facing the respective clean sideof the known filter element. If the filter element is removed from thefilter housing over the cover part of the known design, the filterhousing forms a holding vessel for the dirty oil when the filter elementis changed and no fouled fluid remains within the filter device; thiswould lead to dirt in the hydraulic circuit when the filter device isrestarted. Although with respect to the inserted support elements in theform of support tubes adequate and secure support of the actual filterunits and of the filter material takes place and hence failure of thefilter element is precluded, the cylindrical support tubes on the innerand outer peripheral side have only smooth guide surfaces between whichpassage points for the fluid are formed. Consequently flow through theknown support tubes takes place essentially transversely to theirlongitudinal alignment so that in the process fluid guidance isrestricted, and the known approach cannot be used for special filtrationtasks, for example if the intention is to eliminate fluid from thefilter units with the filter material by drainage.

DE-A-44 30 341 discloses a generic filter element for filtration offluid, with a hollow-cylindrical support element for a cup-shaped fluidfilter which is closed with a removable cover, especially for oil orfuel, with a filter housing into which an interchangeable filter unit isinserted which consists of a length of filter material which is foldedin a star-shape with end disks which are mounted on its two end sides toform a seal, the end disk which is cover-shaped in the installationstate of the filter unit forming a fluid opening. The pertinent supportelement prevents collapse of the filter unit as the fluid stream whichis to be filtered flows through it in one direction, and with the knownapproach it is possible to leave the support element in the filterhousing each time the filter unit is changed, so that it is notnecessary to dispose of the support element which is not subject to weartogether with the filter unit.

In order to achieve improved fluid guidance between the support elementand the filter unit which encloses it, in one especially preferredembodiment provision is made such that the support projections be routedaround the tubular support element in the manner of a 4-lead spiralalong the outside periphery in order to repeatedly deflect the fluidstream around the longitudinal axis of the filter element by 360°. Inthis case it is characteristic for the known embodiment of the supportelement that the support projections have sections with differentpitches. In this way, a parallel arrangement of a total of fourintermediate spaces with the shape of helical lines may be formedbetween the indicated support projections. These intermediate spaces areavailable for directed fluid flow around the outside periphery of thecentral part as far as the fluid overflow openings which are provided inits upper part. Because the support projections which form the channelsrun in a helical path, continuous fluid guidance along the tubularsupport element is prevented and as a result of the aforementionedrepeated deflection of the fluid flow, an unfavorable fluid flowcharacteristic occurs between the support element and the filter unitwhich encloses it and which is supported on it.

A comparable arrangement is disclosed according to one embodiment asshown in FIG. 3 in WO 01/91881, in this known approach only a helicalchannel guide which encompasses the support element being used for fluidtransport and for supporting the filter unit within the filter housing.Here repeated deflection of the fluid flow around the longitudinal axisof the filter element is unfavorable in terms of energy expenditure andthe support projections of the support element which form the helicalchannel form only a small support surface for the filter unit which isto be supported, so that in this respect reliable support, especiallyfor larger fluid difference pressures, does not take place.

Furthermore, JP-20011293312 A discloses a filter device with a filterunit which is located in a filter housing and in which the supportelement is provided with a plurality of flow channels which are locatedon the outer peripheral side, which run in a straight line and which areused for fluid transport within the filter device when oriented to thelongitudinal axis of the filter element. In spite of the good supportfor the filter unit which can be achieved hereby, filtration performanceis adversely affected as a result of the known linear fluid guidance.

On the basis of this prior art, the object of the invention is to devisea filter element for filtration of fluid, which permits reliableoperation without failure and with which high filtration performance canbe achieved in a manner which is favorable in terms of energyexpenditure. This object is attained by a filter element with thefeatures specified in claim 1 in its entirety.

In that, as specified in the characterizing part of claim 1, thechannels extend continuously without repeated deflections of the fluidstream along the respective support element and in that the channelsonly partially encompass the respective support element with theformation of a twisting guide, the support element with its longitudinalribs which border the spiral channels allows reliable support of thefilter unit with the assigned filter material during operation of thefilter element, and at the same time as a result of the plurality offluid channels which accordingly are possible large amounts of the fluidwhich is to be filtered can flow through the filter unit in thedirection of the support element.

Since the channels with their longitudinal ribs which border them areguided in spiral tracks in a twisting guide without repeated deflectionalong the support tube, it has been shown that such a spiral twistingguide accordingly leads to low friction losses in fluid guidance; thisin turn has a beneficial effect on the behavior of flow thorough thefilter element as claimed in the invention in terms of energyexpenditure. The pertinent twisting guide is made in the manner of thehelical rifling of low incline, as is made in the barrel of a firearm,by which the round is brought into stabilizing rotary motion. Theindicated twisting guide therefore allows channel guidance which extendsfree of repeated deflections along the respective support element in atilted alignment to its longitudinal axis. With the filter elementdesign as claimed in the invention moreover different filter tasks canalso be carried out, for example when a copious amount of fluid must bequickly removed from the filter unit of the element by draining toimprove the filtration performance.

Preferably the respective support element is formed from a support tubeand the respective channels are bordered by the longitudinal ribs of thesupport tube which project laterally; this benefits linear fluidguidance and the cavity and flow losses can be kept low in such a waythat the filter element in terms of flow behavior can be described asfavorable in terms of energy expenditure.

If in one preferred embodiment of the filter element as claimed in theinvention, the channels are located both on the inner and also outerperipheral side on the support tube, the fluid transport performance canbe further improved and in this way a support possibility can be foundin the two directions for the bordering filter material.

In another preferred embodiment of the filter element as claimed in theinvention, the longitudinal ribs may be seated on the support tube inthe manner of crosspieces or the longitudinal ribs which are locateddirectly adjacent are connected in pairs to one another and on the outerperipheral side form a support surface and on the inner peripheral sideform the base of the groove of the individual channels. Compared to thecrosspiece-like arrangement of the longitudinal ribs, the outerperipheral-side support surface in the same manner as the groove base onthe inner peripheral side offers a widened contact surface so thatconsequently improved support for the filter material of the respectivefilter unit is achieved.

Other advantageous embodiments of the filter element as claimed in theinvention are specified in the other dependent claims.

Reference will now be made to the drawing of the filter element asclaimed in the invention and in which in schematic form and not drawn toscale

FIG. 1 is a section of a longitudinal view through the filter element;

FIG. 2 in schematic form is a top view of the filter element as shown inFIG. 1 without the cover parts and without the filter units, and

FIG. 3 in schematic form is a view of a modified embodiment of onesupport element in the form of a support tube relative to the insertedsupport elements as shown in FIG. 2.

One embodiment of the filter element as claimed in the invention isshown in FIG. 1 in the manner of a longitudinal section. The filterelement is used for filtration of fluids, especially in the form ofdirty hydraulic oil or the like. Three filter units 12, 14, 16 arearranged around the longitudinal axis 10 of the filter elementconcentrically to the latter. For the sake of clarity the filter unit 12which is located outermost has been shown only with half its axiallength. The indicated filter units 12, 14, 16 each have a radialdistance between each other and on the inside are held by two coverparts 18, 20 designed as end caps. In particular, the ends of the filterunits 12, 14, 16 can be joined to the two cover parts 18, 20 by way of abed of adhesive or the like.

In the cover parts 18, 20 there is a fluid guide which is designated asa whole as 22. The type of fluid passage and the type of internal fluidguide 22 are shown in FIG. 1 with the corresponding arrows, flow takingplace through the filter element in the direction of the arrow.Furthermore, in the respective distance between the filter units 12, 14,16 a support element 24, 26 is placed as a support and/or drainage tube.Depending on the flow direction of the fluid which is to be filtered(unfiltered material), at least some of the filter units 12 and 14 whichborder adjacently are thus effectively supported in the flow-throughdirection by way of the assignable support elements 24, 26 in order thusto prevent bulging of the respective filter unit 12, 14, 16.Furthermore, the support elements 24, 26 are provided with channels 28as another part of the internal fluid guide 22. The pertinent channels28 are shown in FIG. 2 for the two support elements 24 and 26 for oneembodiment on the support elements 24, 26.

The respective filter unit 12, 14, 16 is formed from a cylindricalfilter mat, and the pertinent filter mat may be wound or folded andconsists of a filter material which is conventional in this field. Asfurthermore follows from FIG. 1, the respective filter mat is providedwith a uniform linear dimension, like the other inserted cylindricalfilter mats, measured in the direction of the longitudinal axis 10 ofthe filter element. The filter unit 16 which is located innermost viewedin the direction of looking at FIGS. 1 and 2 is supported on the innerperipheral side on a support tube 30 with an interior which is connectedto the clean side 32 of the filter element (see FIG. 1). The structureof the pertinent support tube 30 is of conventional design and is knownfrom another connection, said support tube consisting of individualannular segments 34 which are located on top of one another, whichborder the fluid passages for passage of the filtrate between oneanother, and the support crosspieces 36 which border over threeidentical angles between themselves being kept at a distance to oneanother (see FIG. 2). Thus the inner, conventionally made support tube30 supports the innermost filter unit 16 when flow-through takes placein the direction from the outside (compare arrow 22) to the inside. Inthe embodiment as shown in FIG. 2 there are a total of 40 fluid channels28 both on the inner and also the outer peripheral side on each of thetwo support elements 24, 26. Preferably in any case always more than 20fluid channels 28 are used for one of the indicated support elements 24,26. Thus, in the embodiment as shown in FIG. 3 which will be detailedbelow, there are 24 channels 28 respectively both on the inner and alsothe outer peripheral side.

The cover part 18 which is the upper one when viewed in the direction oflooking at FIG. 1 consists essentially of two parts 38, 40 which caneach be joined integrally to one another. The upper part 38 is providedwith a mountable handle 42 designed as a grip in order to remove forexample the filter element from the filter housing of the filter device(not shown) when the filter element has been used up and so to replaceit with a new filter element. The fouled and unfiltered fluid(unfiltered material) can be supplied to the filter element by way ofinlets 44 designed as holes which are arranged diametrically to thelongitudinal axis 10, the pertinent inlets 44 extending through the twoparts 38 and 40 of the upper cover part 18. The upper cover part 40 iselongated downward in the middle as a shoulder and in the middleencloses a central channel 46 which leads to the clean side 32 withinthe filter element by way of the support tube 30.

Furthermore, in the upper cover part 18, as part of the internal fluidguide 22 there are flow channels (not shown) which make it possible, asshown in the partial representation in FIG. 1, to accommodate alreadyfiltered fluid by way of the filter units 12 and 14 and to transport itin the direction of the central channel 46 to the clean side 32 of thefilter element. The cover part 20 which is the lower one when viewed inthe direction of looking at FIG. 1 is designed accordingly like theupper cover part 18, and instead of the handle 42 however the lowercover part 20 has the clean side 32 of the filter element which isenclosed by a jacket connection 48.

As shown particularly in FIG. 2 which relates to one embodiment of thefilter element, the two support elements 24 and 26 are made cylindricaland along their outer and inner periphery each have longitudinalchannels 56, 58, 60, and 62 which can be regarded as part of theinternal fluid guide 22. The respective longitudinal channel 56, 58, 60,and 62 of the assignable support element 24 and 26 is equidistant to thenext following longitudinal channel on the inside or outside of thepertinent support element, the longitudinal channels 56, 58, 60, and 62along the longitudinal axis 10 of the filter element having a twist suchthat a type of twisting guide for the fluid which is to be transportedis achieved.

The indicated filter element is used for installation in a conventionalfilter device which has an inlet point for the filtered fluid [sic] andan outlet point for the filtered fluid (filtrate) (not shown).

In order to detail the operation of the filter element as claimed in theinvention, this is shown using the arrows in FIG. 1.

When viewed in the direction of looking at FIG. 1, to the right of thelongitudinal axis 10 of the filter element the internal fluid guide 22is detailed. By way of an inlet point which is not detailed in thefilter housing for the filter element shown in FIG. 1, the unfilteredmaterial flows from the outside to the inside through the first filterunit. The contaminants present in the unfiltered material are thenretained in the first filter unit 12 and the fluid flow of filtrate istaken up on all sides and on the outer peripheral side by way of theouter longitudinal channels 56 of the first support element 24 and isdischarged in equal parts up and down into the upper cover part 18 andinto the lower cover part 20. The filtrate is then taken up into therespective bottom part by way of the internal fluid guide 22 in thecover parts and transported in the direction of the central channel 46,from where discharge takes place by way of the middle of the supporttube 30 between the support crosspieces 36 in the direction of the cleanside 32. At the same time, in the direction of the arrows 66 additionalunfiltered material is introduced into the filter element by way of thefilter housing which is not detailed, specifically by way of the inlets44 which are separated fluid-tight from the other internal fluid guideswithin the cover parts 18, 20.

The unfiltered material which is supplied by way of the inlets 44travels by way of the upper cover part 18 and the lower cover part 20into the longitudinal channels 60 and 62 of the second support element26 and the pertinent unfiltered material is then sent uniformly in bothdirections once through the inner third filter unit 16 and once throughthe middle filter unit 14. The latter stream of filtrate is thentransported in turn by way of the inner guide channels 58 of the firstsupport element 24 into the cover parts 18, 20 and in turn travels byway of the internal cover fluid guide to the clean side 32 of the filterelement, as described. The other branched filtrate flow then travels byway of the third filter unit 16 into the interior of the support tube 30and from there likewise to the clean side 32 of the filter element. Thepertinent internal fluid guide 22 is shown by way of example for oneflow path, this taking place, as described, radially on the outerperipheral side along the individual filter units 12, 14, 16 and thesupport elements 24, 26.

By the concentric arrangement of several filter mats around theaforementioned support tube 30, one drainage tube in the form of supportelements 24, 26 each being located between two filter mats, theavailable installation space in the filter housing of a filter device(not shown) is more effectively used, whereby an increase of thedirt-holding capacity can be achieved and the flow resistance of thefilter element is accordingly reduced by the enlargement of the filterarea so that the entire filter element can be characterized as favorablein terms of energy expenditure for the throughflow process. As shown,some of the drainage tubes are designed to supply the filtered fluid inthe two end caps in the form of cover parts 18, 20, whereas another partis designed to supply the unfiltered fluid (unfiltered material) fromthe two end caps to the filter mats. The indicated drainage tubes assupport elements 24, 26 which in the same way as the support tube 30form a support function for the assignable filter units 12, 14, 16, canbe made as shown in FIG. 3 also in the manner of a corrugated tube oralso as rings which are stacked on top of one another with holes (notshown). Due to the indicated arrangement as shown in FIG. 1, it appliesto each drainage tube that the pressure on its inside corresponds to thepressure on its outside so that for the filter element overall apressure-compensated arrangement is achieved; this has a beneficialeffect on the service life of the filter element.

In a different embodiment of a support element 24, 26 as shown in FIG.3, the longitudinal ribs 50, which are arranged directly adjacent, areconnected to one another in pairs and on the outer peripheral side forma support surface 68 and on the inner peripheral side a groove base 70of the individual channels 28. Opposite the crosspiece ends of thelongitudinal ribs 50 according to the first embodiment as shown in FIG.2, the supporting contact surfaces for the assignable filter units 12,14, 16 are consequently elevated by way of the support surfaces 68 andthe groove base 70; this suggests that the embodiment as shown in FIG. 3is especially well suited if the pertinent filter units and filtermaterials are exposed to high compressive stresses and compressivestress cycles as the fluid flows through.

The embodiment as shown in FIG. 3 can be combined with the embodiment asshown in FIG. 2 for a filter element, for example by the embodiment asshown in FIG. 3 forming the innermost support element 26 and thearrangement with the raised longitudinal ribs 50 forming the outermostsupport element 24. But two or more support elements according to theembodiment as shown in FIG. 3 arranged concentrically to one another canalso form a drainage tube system for a filter element. If depending onthe filtration task this should be necessary, the respective supportelement 24, 26 can also be provided with perforations which are notdetailed, in order to achieve fluid passage transversely to thelongitudinal axis 10 of the filter element in this way. The pertinentperforations (not shown) may penetrate the channels 28, but also in theembodiment as shown in FIG. 3 the support surface 68 along with thegroove base 70. The support element 24, 26 which is designed as acorrugated tube as shown in FIG. 3 can also be easily obtained as anextrusion part from plastic material.

1. a filter element for filtering fluids with at least one filter unit(12, 14, 16) which is arranged concentrically around its longitudinalaxis (10), and which is supported in the direction of the respectivethroughflow with the fluid stream on at least one support element (24,26, 30), at least some of the support elements (24, 26) being providedat least on their side facing the filter unit (12, 14, 16) with channels(28) for fluid guidance (22), the channels (28) extending with theirlongitudinal ribs (50) which border them in spiral tracks along thesupport element (24, 26), and the respective channel (28) with its twofree ends emerging on the opposing ends of the respective supportelement (24, 26), characterized in that the channels (28) extendcontinuously without repeated deflections of the fluid stream along therespective support element and that the channels (28) only partiallyencompass the respective support element (24, 28) with the formation ofa twisting guide for the fluid flow:
 2. The filter element as claimed inclaim 1, wherein the respective support element (24, 26, 30) is formedfrom a support tube and wherein the respective channels (28) arebordered laterally by the projecting longitudinal ribs (50) of thesupport tube.
 3. The filter element as claimed in claim 2, wherein thechannels (28) are located both on the inner and outer peripheral side onthe support tube (24, 26).
 4. The filter element as claimed in claim 1,wherein the longitudinal ribs (50) are seated as crosspieces on thesupport tube (24, 26) or wherein the longitudinal ribs (50) which arelocated directly adjacent connected in pairs to one another on the outerperipheral side form a support surface (68) and on the inner peripheralside form the base (70) of the groove of the individual channels (28).5. The filter element as claimed in claim 1, wherein there are a totalof three support elements (24, 26, 30) and three filter units (12, 14,16) which are arranged in an alternating sequence concentrically aroundthe longitudinal axis (10) of the filter element.
 6. The filter elementas claimed in claim 5, wherein the innermost support element (30) has asupport tube with passages as the channel guide for the fluid flow. 7.The filter element as claimed in claim 5, wherein the fluid stream mayflow through the innermost and the outermost filter unit (16, 12) fromthe outside to the inside in the direction to the clean side (32) of thefilter element and wherein flow is incident on the filter unit (14)which lies in between from the two sides to the inside and outside. 8.The filter element as claimed in claim 1, wherein the respective filterunit (12, 14, 16) is formed from a cylindrical filter mat and whereinall filter mats have essentially the same linear dimensions in the axialdirection to the longitudinal axis (10).
 9. The filter element asclaimed in claim 1, wherein the support elements (24, 26, 30) and thefilter units (12, 14, 16) are arranged concentrically to thelongitudinal axis of the filter element.
 10. The filter element asclaimed in claim 1, wherein at least 20 channels (28) which are locatedon one of the support elements (24, 26, 30) form a common fluid guideand wherein the respective channel (28) has a tilt of the twisting guidebetween 10° to 30°, preferably 15°, relative to the axis which isparallel to the longitudinal axis of the filter element.